Generally speaking ... to turn off mirroring you run:
- sp_configure 'disable disk mirroring',1
- since this is a static setting you will need to bounce the dataserver
However, in your case this will fail because you currently have some mirrored devices. So, before you can disable mirroring you must first unmirror all currently mirrored devices (see the 'disk unmirror' command).
Obviously (?) you'll want to find out a) why those devices are currently mirrored and b) what would be the ramifications if you unmirrored said devices